The present invention relates to ink jet printers and, more particularly, to a printer producing a plurality of jet drop streams directed toward a print receiving medium. The jet drop streams are positioned along a row which is inclined with respect to the direction of movement of the medium and the jet drop streams are deflected in a direction substantially perpendicular to the direction of movement of the print receiving medium so that each stream deposits drops at a plurality of adjacent, laterally spaced print positions on the medium.
Ink jet printers of the type shown in U.S. Pat. No. 3,701,998, issued Oct. 31, 1972, to Mathis, include a print head having one or more rows of orifices which receive an electrically conductive fluid from a pressurized fluid manifold and eject the fluid in a plurality of jet drop streams. Graphic reproduction in recorders of this type is accomplished by selectively charging and deflecting some of the drops in each of the streams and depositing the uncharged drops on a moving web of paper or other material. In the Mathis printer, the direction of web movement is substantially perpendicular to the rows of orifices. Charging of the drops is accomplished by application of charge control signals to charging electrodes near the jet drop streams. As the drops separate from the fluid filaments emerging from each of the orifices, they carry a portion of the charge induced in the filament tips by the charging electrodes. Thereafter, the drops pass through an electrostatic field which has no effect upon the uncharged drops but which causes the charged drops to be deflected. Drops which are not to be printed are charged sufficiently to be deflected to drop catchers.
One problem with printers of this type, and with all types of ink jet printers, has been attaining sufficient image resolution. Since a discrete number of drops are applied to form the images on the print receiving medium, it is clear that image definition may be improved by increasing the number of drops deposited. If, however, each jet drop stream deposits drops of only one print position on the print receiving medium, the number of drops per unit width and, therefore, the resolution of an image in the direction transverse to the direction of movement of the medium is limited by the number of jet drop streams. This, in turn, is limited in a printer having a simple row of jet drop streams by the minimum dimensions required between adjacent orifices from which the jet drop streams emerge. The approach taken in the Mathis printer is to provide two rows of jet drop streams which are staggered, such that the print positions on the print medium serviced by one of the rows interlace with the print positions serviced by the other of the rows. The charging of the drops in the two rows is timed such that printing from the two rows of jet drop streams is maintained in registration.
Another approach which has been taken is to deflect drops from each of the jet drop streams to a plurality of adjacent print positions, such that each jet drop stream deposits drops along a number of adjacent print lines across the width of the print receiving medium. This has been accomplished in several ways. In U.S. Pat. No. 3,298,030, issued Jan. 10, 1967, to Lewis et al, an ink jet printer is disclosed in which deflection of each of the jet drop streams is produced by a raster scan signal supplied to a pair of parallel deflection electrode plates positioned laterally to either side of each of the jets. It will be appreciated that since a pair of deflection electrode plates and a catcher structure must be positioned between adjacent jet drop stream, the minimum interjet spacing in the Lewis et al printer and, therefore, the print image resolution in a direction perpendicular to that of the print receiving medium, is severely limited.
Similarly, U.S. Pat. No. 3,739,395, issued June 12, 1973, to King; U.S. Pat. No. 3,641,588, issued Feb. 8, 1972, to Metz; and U.S. Pat. No. 4,123,760, issued Oct. 31, 1978, to Hou, disclose ink jet devices having a row of jet drop streams extending generally perpendicular to the direction of movement of a print receiving medium, and in which drops are deflected in a direction oblique to the row such that the drops may service more than one print position. The King, Metz, and Hou printers all require deflection electrode plates interposed between adjacent jet drop streams, however, and therefore the minimum interjet spacing and resulting print resolution are limited.
Another approach which has been taken to increase the print image resolution produced by an ink jet printer is to provide one or more rows of jet drop streams which extend across the print receiving medium at an angle to the direction of movement of the medium. Such printers are shown in U.S. Pat. No. 4,010,477, issued Mar. 1, 1977, to Frey; U.S. Pat. No. 4,085,409, issued Apr. 18, 1978, to Paranjpe; U.S. Pat. No. 4,122,458, issued Oct. 24, 1978, to Paranjpe; and U.S. Pat. No. 4,048,639, issued Sept. 13, 1977, to Walsh et al. In the Frey '477 printer, a plurality of parallel angularly arranged jet drop stream rows are provided, with each jet drop stream servicing only a single print position on the print receiving medium.
The drops in the one or more rows of jet drop streams produced by the Paranjpe '409, Paranjpe '458, and Walsh et al printers are deflected in a direction substantially perpendicular to the row or rows of jet drop streams. As a consequence, the deflection electrode structure for producing drop deflection extends adjacent the row or rows of jet drop streams and the minimum interjet spacing is not limited by the need to interpose deflection structure between adjacent jets.
In such printers, where the charged drops are deflected in a direction substantially perpendicular to the jet drop stream rows and the rows extend obliquely with respect to the direction of paper movement, however, it will be appreciated that each jet drop stream is deflected both laterally, widthwise across the moving web, and longitudinally in the direction of web movement. In order to provide for a given amount of lateral deflection, therefore, it is necessary to deflect a drop in a direction perpendicular to the row of jets by a much greater distance. Such substantial deflection distances may be difficult to obtain if the print head construction limits the charge to mass ratio of the charged drops or the strength of the deflection fields. Additionally, if the angle of inclination of the row of jets with respect to the direction of movement of the print receiving medium is severe, a relatively long row of jets may be required to span even a narrow print receiving medium. Finally, since each of the print positions associated with the various print lines across the width of the print receiving medium in such a printer is displaced longitudinally along the print receiving medium from other print positions, complicated data handling and delay circuits are required for providing control signals to the jet charge electrodes at appropriate times to produce the desired print image.
U.S. Pat. No. 4,091,390, issued May 23, 1978, to Smith et al, discloses a recording device having an inclined row of ink jet nozzles which produce a row of jet drop streams, the drops of which are deflected by a single pair of planar electrostatic deflection plates common to all the nozzles and extending parallel to the row. The Smith reference teaches deflecting the drops in each of the jets in a direction perpendicular to the jet row to service a number of print lines across the print receiving medium, as well as deflecting the drops from the jets at an angle with respect to the inclined row of jet drop streams in order to compensate for the movement of the print receiving medium during the deposit of successive drops from each of the jet drops.
U.S. Pat. No. 4,060,804, issued Nov. 29, 1977, to Yamada, discloses an ink jet recording device having two jets which are displaced laterally and longitudinally above a moving print receiving medium, with each of the jet drop streams being deflected substantially perpendicularly with respect to the direction of movement of the medium so as to deposit drops at a number of laterally displaced print positions. Although deflecting the jet drop streams substantially perpendicular to the direction of movement of the print receiving medium, the Yamada printer is limited by virtue of its construction to a two-jet printer. Therefore, the Yamada printer is limited to printing a print receiving medium of a width which may be serviced by only two jets.
Another problem encountered with ink jet printers is that of providing adequate catching of drops which are directed into catch trajectories such that the drops do not strike a print receiving medium. A number of different catcher designs have been utilized in prior art printers but, typically, these catchers must be precisely positioned with respect to the jet drop streams. Additionally, fabrication of such catchers may be involved. One type of catcher, as illustrated in U.S. Pat. No. 3,656,174, issued Apr. 11, 1972, to Robertson, utilizes an apertured plate which defines an opening through which undeflected drops pass. Deflected drops strike the plate adjacent the opening, and are thereafter removed by appropriate fluid suction apparatus. Such apertured plates have generally been of only limited success, however, since ink drops and mist may tend to collect on the bottom of the plate and thereafter may drip onto the print receiving medium. It is desirable to utilize such an apertured plate catching arrangement, however, due to the simplicity of its construction and the fact that it does not add substantially to the thickness of the printer print head.
Accordingly, it is seen that there is a need for an ink jet printer, having an inclined row of jets, in which each of the jet drop streams may be deflected to service a number of adjacent print positions without requiring deflection electrode apparatus to be interposed between adjacent jets and in which each of the jet drop stream is deflected substantially perpendicularly with respect to the direction of movement of the print receiving medium. Additionally, there is a need for an improved catcher arrangement for an ink jet printer utilizing an apertured catcher plate in which ink is prevented from dropping from the plate onto the print receiving medium.